Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, a conventional magnetic tunneling junction (MTJ) may be used in a conventional STT-MRAM. The conventional MTJ typically resides on a substrate. The conventional MTJ includes at least a conventional pinned layer, a conventional free layer and a conventional nonmagnetic tunneling barrier layer between the conventional pinned and free layers. A bottom contact below the conventional MTJ and a top contact on the conventional MTJ may be used to drive current through the conventional MTJ in a current-perpendicular-to-plane (CPP) direction. The conventional pinned layer and the conventional free layer are magnetic. The magnetization of the conventional pinned layer is fixed, or pinned, in a particular direction. The conventional free layer has a changeable magnetization.
To switch the magnetization of the conventional free layer, a current is driven through the MTJ perpendicular to plane. When a sufficient current is driven from the top contact to the bottom contact, the magnetization of the conventional free layer may switch to be in one direction with respect to the magnetization of a conventional bottom pinned layer. When a sufficient current is driven from the bottom contact to the top contact, the magnetization of the free layer may switch to be in the opposite direction with respect to the magnetization of the bottom pinned layer. The differences in magnetic configurations correspond to different magnetoresistances and thus different logical states of the conventional MTJ.
To fabricate conventional MTJs, a stack of layers is typically provided. This stack includes any seed layer(s), the pinned layer, the nonmagnetic spacer layer, the free layer and capping layer(s). In the case of a dual MTJ, the stack also includes the additional nonmagnetic spacer layer and pinned layer. These layers are full film deposited on the substrate. A mask covering regions of the substrate on which the MTJs are to be formed is provided. The stack is then etched to define the magnetic junction. Fabrication of the magnetic device may be completed, for example by refilling the region between the MTJs and providing electrical contact to the MTJs.
The current trend in memory technology is to higher recording densities. To increase the areal density of magnetic memories, MTJs are spaced closer together. For example, the height of the MTJ stack may be on the order of the distance between stack. As a result, fabrication of MTJs at higher densities may be challenging. Accordingly, what is needed is a method and system that may extend the spin transfer torque based memories to higher densities. The method and system described herein address such a need.